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package cryptfs
// Implements cipher.AEAD with OpenSSL backend
import (
"bytes"
"github.com/spacemonkeygo/openssl"
)
// Supports all nonce sizes
type opensslGCM struct {
key []byte
}
func (be opensslGCM) Overhead() int {
return AUTH_TAG_LEN
}
func (be opensslGCM) NonceSize() int {
// We support any nonce size
return -1
}
// Seal encrypts and authenticates plaintext, authenticates the
// additional data and appends the result to dst, returning the updated
// slice. opensslGCM supports any nonce size.
func (be opensslGCM) Seal(dst, nonce, plaintext, data []byte) []byte {
// Preallocate output buffer
var cipherBuf bytes.Buffer
cipherBuf.Grow(len(dst) + len(plaintext) + AUTH_TAG_LEN)
// Output will be appended to dst
cipherBuf.Write(dst)
ectx, err := openssl.NewGCMEncryptionCipherCtx(KEY_LEN*8, nil, be.key, nonce)
if err != nil {
panic(err)
}
err = ectx.ExtraData(data)
if err != nil {
panic(err)
}
part, err := ectx.EncryptUpdate(plaintext)
if err != nil {
panic(err)
}
cipherBuf.Write(part)
part, err = ectx.EncryptFinal()
if err != nil {
panic(err)
}
cipherBuf.Write(part)
part, err = ectx.GetTag()
if err != nil {
panic(err)
}
cipherBuf.Write(part)
return cipherBuf.Bytes()
}
// Open decrypts and authenticates ciphertext, authenticates the
// additional data and, if successful, appends the resulting plaintext
// to dst, returning the updated slice. The nonce must be NonceSize()
// bytes long and both it and the additional data must match the
// value passed to Seal.
//
// The ciphertext and dst may alias exactly or not at all.
func (be opensslGCM) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
l := len(ciphertext)
tag := ciphertext[l-AUTH_TAG_LEN : l]
ciphertext = ciphertext[0 : l-AUTH_TAG_LEN]
plainBuf := bytes.NewBuffer(dst)
dctx, err := openssl.NewGCMDecryptionCipherCtx(KEY_LEN*8, nil, be.key, nonce)
if err != nil {
return nil, err
}
err = dctx.ExtraData(data)
if err != nil {
return nil, err
}
part, err := dctx.DecryptUpdate(ciphertext)
if err != nil {
return nil, err
}
plainBuf.Write(part)
err = dctx.SetTag(tag)
if err != nil {
return nil, err
}
part, err = dctx.DecryptFinal()
if err != nil {
return nil, err
}
plainBuf.Write(part)
return plainBuf.Bytes(), nil
}
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